Supplementing our ongoing work on regulatory sites in pro and eukaryotic genomes, the structures of the genes for heavy chains immunoglobulins of mouse will be determined using recombinant DNA techniques. cDNA copies of messenger RNAs for mouse gamma, alpha and Mu chains will be cloned into plasmids. These will be verified by DNA sequencing using the Maxam Gilbert technique and the Sanger dideoxy technique. DNA will be labelled with 32P and used as probe to isolate clones directly from the genome of mouse. The sequences of the genomic clones will be obtained and compared with the cDNA sequences. These data should provide an insight into the regulation of the immune system of mouse.